According to the cameraman:
Initial velocity: 30 km/hr = 8.33 m/s
Final velocity: -(45 - 20) = -25 km/hr = -6.94 m/s²
a = (-6.94 - 8.33)/2
a = -7.64 m/s²
The direction is opposite to the motion of the car, that is, East.
According to the crew member on ground:
Initial velocity: 20 + 30 = 50 km/hr = 13.89 m/s
Final velocity: -45 km/hr = -12.5 m/s
a = (-12.5 - 13.89) / 2
a = -13.2 m/s²
The direction is the same, East.
In most cases the temperature must increase for thermal expansion to occur. Most substances expand as temperature increases because the atoms or molecules vibrate faster as temperature increases and experience greater separation.
When waves travel across strings, the larger the tension of the string the faster the velocity of the wave. This is because of the equation:
v = the square root of (T/(m/L)) where T is the tension, m the mass of the string, and L the length of the string
Hope this helps!